The present invention relates to a method of manufacturing integrated optical devices and testing their performance. The invention is particularly concerned with the manufacture and testing of integrated optical components which have optical fiber pigtails.
Integrated optical components with fiber pigtails are well known. See, Dohan et al. U.S. Pat. No. 4,765,702, Beguin U.S. Pat. No. 4,933,262 and Dannoux et al. U.S. Pat. No. 4,943,130. These components have been produced using ion exchange techniques. Dannoux et al. U.S. Pat. No. 4,979,970 is directed to a method of manufacturing an integrated optical component comprising, for example, a 2.times.2 optical waveguide proximity coupler, each end of the coupler having two optical fibers (pigtails) attached in optical alignment with two ion-diffused waveguides within a glass substrate. FIGS. 2a and 2b of the present application depict a prior art 1.times.2 splitter/combiner of a similar structure.
Pigtailing is a critical step in the manufacture of such integrated optical components. This step includes both the alignment of the optical fiber waveguide paths with the ion-diffused waveguide paths, and the attachment of the fiber pigtail ends to the component surface. The alignment must be very precise, and the attachment must assure the stability of the alignment during environmental variations (especially temperature fluctuations). Precise alignment is difficult, especially for single mode waveguides, whose core diameters are in the range of 5-10 microns.
As described in Dannoux et al. U.S. Pat. No. 4,979,970, the fiber pigtail ends may be precisely aligned with the optical circuit paths using a micromanipulator, after initial approximate alignment by means of an external jig referenced to the component body (col. 4, lines 20-24 and 41-50). The micromanipulator is typically used in conjunction with optical detection means to provide active alignment--the micromanipulator moves the fiber end back and forth in the vicinity of the component waveguide output port, until the detected optical signal is at a maximum. The precision of the micromanipulator movements is on the order of a tenth of a micron.
Once precise alignment is achieved by means of a micromanipulator, a glue joint is applied to the junction of the fiber and the component surface, and the glue is hardened (for example, by ultraviolet light curing) to attach the fiber pigtail to the component.
Referring to FIGS. 2a and 2b, optical component 30 includes waveguide combiner/splitter 25 separated by transverse exit groove 21 from bare fiber attachment support 22 and coated fiber attachment support 23. Transverse exit groove 21 forms alignment space 20, which provides room for the micromanipulator to hold and move the optical fibers. To carry put active alignment, two micromanipulators may be used simultaneously to align input fiber 27 and first output fiber 28. Once fiber 27 and 28 are thus aligned, their precise alignment is maintained by glue joints 26 and 26a, and the fibers are securely attached to the component by adhesive means 24 and 24a. The operation is repeated for fiber 29. For a 1.times.2 device all three fibers may be aligned and attached simultaneously, depending on the sophistication of the micromanipulators and of the software driving them.
In prior art techniques (see FIGS. 1a-1c), the waveguide paths for numerous components are created simultaneously in a single wafer 5 by photolithographic techniques. Thereafter, the components are grooved (FIG. 1b) and separated (FIG. 1c), and all further operations, such as pigtailing and packaging (assembly), measurement, characterization and testing are performed separately on the individual components.
In the prior art fiber pigtailing process described above there are two separate alignment steps for each passive optical component: 1) initial approximate alignment (on the order of +/-20 microns); and 2) precision alignment (on the order of +/-0.5 micron). This is a costly and time-consuming drawback. The initial approximate alignment requires the most time, as the side surface of the component is often a poor reference point. Once the waveguide output port for one of the fibers on the multi-fiber side of a single device has been precisely located, the other output port or ports on this side of this device can be located without repeating the approximate alignment step. This is because the waveguide paths are very precisely aligned with one another in the photolithographic masking stages of the process (better than 1 micron precision). However, the time-consuming approximate alignment step must be repeated for each new device.
FIGS. 1a, 1b and 1c depict the individual component formation process of the prior art. FIG. 1a depicts an integrated optics wafer 5 in which the waveguide paths have been formed (paths are not shown) for tens to hundreds of individual components. FIG. 1b depicts a wafer after fiber attachment supports 2/3 and 2a/3a and transverse exit grooves 1 and 1a have been formed in the wafer, typically by grinding and typically after the waveguide paths have been formed in the wafer. The wafer is thereafter separated into individual components 10 by conventional methods.
Within a single wafer, there is precise alignment between the waveguide paths of different components, due to the inherent precision of the photolithographic process. However, when the wafer is separated into individual components, this precise alignment is destroyed. It is therefore an object of the present invention to preserve the precise alignment of the initial photolithographic process until the fiber pigtails are securely attached to the integrated optical components.
Other steps in prior art manufacturing processes are also costly and time consuming when carried out separately for each individual component. For example, preparation and handling of individual optical fibers for attachment to numerous individual devices requires numerous separate repetitive operations, such as stripping and fiber end face preparation (reduction of back reflections). This is especially true in the alignment and measurement stages of the manufacturing process, where the fiber ends opposite the component must be separately located in order to inject or detect an optical signal. It is therefore another object of the present invention to perform the manufacturing operations of assembly, packaging and measurement on a large number of components at a time, rather than separately on individual components, obviating the necessity of creating a separate optical location and connection with the free end of each fiber pigtail.
In addition, separate handling of individual components in the early stages of the manufacturing process is also time-consuming and costly. It is therefore an object of the present invention to maintain the compact integrity of the integrated optics wafer as long as possible in the manufacture and testing of integrated optical components.